Fiat 1995 Brava, Service Manual

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B r a k i n g s y s t e m
Bravo-Brava
Anti-lock braking system
33.
The control unit (1) is supplied:
- directly from the battery (+VB) on pins
9 and 25, through a 60A fuse (2);
- under ignition key (+15) on pin 23,
through a 10A fuse (3).
P4A0SAD01
FAULT DIAGNOSIS
The system has a self-test function which checks if there are any faults on the following components:
- wheel rpm sensors (4 sensors);
- input solenoids (4 solenoids);
- output solenoids (4 solenoids).
If a malfunction is identified, the control unit's safety circuit excludes the A.B.S. system, nevertheless
ensuring normal operation of the conventional braking system.
When the A.B.S. system is switched off, this is'indicated to the driver by the warning light on the instru-
ment panel coming on. For safety reasons, the electronic control unit, by means of two microprocessors,
controls all the logic functions, its software and all the input signals.
If the two microprocessors receive identical input signals, they supply identical output signals.
If there is a logic discrepancy between input signals and output response over a certain period of time,
the safety system detects the fault and the A.B.S. is de-activated.
The electronic control unit also has a safety circuit which monitors the efficiency of the system before
every start-up and during driving.
The safety circuit carries out the following self-tests:
1. after the ignition has been switched on and for about 2 seconds, it checks the operation of the control
unit, the relays which operate the solenoids and the connection of the sensors;
2. after the engine has started, as soon as the speed of 6 km/h is exceeded, it activates the solenoids and
recycling pump for an operating check; it also checks that the 4 speed signals are present;
3. whenever the speed of 24 km/h is exceeded, starting from a standstill, it checks that the 4 speed sig-
nals are present;
4. during driving it continuously checks the peripheral speed of the wheels against the calculated refer-
ence speed, it checks the memory conditions and supervises the operation of the two relays;
5. during driving it constantly checks the battery voltage.
8 Publication no. 506.670